1. Field of the Invention
This invention relates to a Danforth type anchor, an anchor for ships.
2. Description of the Prior Art
Various types of anchors including Danforth type, navy type, mushroom type, holding type and stock type anchors are generally known as anchors for fixing a ship on the water, and a suitable anchor is selected and used in accordance with the particular conditions, such as the dimensions, kind and purpose of use of the ship concerned.
Among these anchors, especially, a Danforth type anchor can be handled simply and stored easily because of its small dimensions and has a low price, so that this anchor is suitable for a comparatively small-sized ship, such as a pleasure fishing vessel, a pleasure boat or the like.
FIG. 6 is a perspective view for describing a Danforth type anchor of the prior art. Referring to this drawing, a reference numeral 31 denotes a shank, 35 fluke, 40 a base unit, and 45 an orientation control rod.
The base unit 40 has a pair of support base plates 36, 36 extending longitudinally in vertical planes in parallel with each other, and is provided by welding with flat plate type flukes 35, 35 so that the flukes project horizontally from the outside of the support base plates 36, 36 and extend forward. Reference numerals 37, 37 denote a pair of secondary guide plates provided on the rear end portions of the support base plates 36, 36 by welding the guide plates to upper and lower edges of the rear end portions unitedly.
The orientation control rod 45 is fixed to the support base plates 36, 36 in a state that it is passed through, and projects horizontally to the outsides of both support base plates 36, 36 in the lateral direction, and extends beyond outer edges of the flukes 35, 35. The shank 31 is inserted at its base end portion in a clearance G between the pair of support base plates 36, 36, and connected to the orientation control rod 45 so that the shank can be turned in both upward and downward directions around the same rod 45 as a pivot. Accordingly, the shank 31 is supported so that it can be turned vertically in a vertical plane passing through the clearance G between the two flukes 35, 35. A reference numeral 32 denotes a shank ring.
The angular range of pivotal movement of the shank 31 is the range between limits at which the shank engages the front edges of the upper and lower secondary guide plates 37, 37, and, usually, the angular range corresponds to the sum of the first angular range between a plane of a reference direction coincident with the direction in which the flukes 35, 35 extend and a plane, for example, about 45.degree. from the plane of the reference direction in the upward direction, and the second angular range between the plane of the reference direction and a plane about 45.degree. from the reference direction in the downward direction, i.e. an angular range of about 90.degree. in total centering around the plane of the reference direction. The shank 31 is unable to turn beyond this angular range.
The Danforth type anchor 30 of such a construction is used as shown in FIG. 7 by joining one end of a metal chain 33 to the shank ring 32 at a front end of the shank 31 thereof, while a mooring rope 34 extending from a ship is joined to the other end of the metal chain 33. Thus, when the Danforth type anchor with the metal chain 33 and mooring rope 34 joined thereto is cast from a ship into the water, the anchor submerges under water due to its our weight.
When the anchor reaches the bottom of the water, it is laid in a substantially horizontally extending state, in which the orientation control rod 45 extends horizontally and the support base plates 36 of the base unit 40 extend vertically, with either of the surfaces of the flukes 35 constituting an upper surface owing to the function of the orientation control rod 45. In a case where the anchor submerges under water with the flukes 35 extending vertically, one free end of the orientation control rod 45 reaches the bottom of the water first, so that the anchor turns down about this end of the orientation control rod 45 due to the orientation of the center of gravity of the whole anchor. As a result, the anchor on the bottom of the water always assumes an orientation with either one of the surfaces of the flukes 35 constitutes an upper surface due to the function of the secondary guide plates 37.
The operation of the Danforth type anchor is completely the same whether the either of the surfaces of flukes 35 constitutes the upper surface. The reason is that the Danforth type anchor has a laterally symmetric structure with respect to an axis along which the shank 31 extends, and a vertically symmetric structure with respect to a plane in which the flukes 35, 35 extend.
On the bottom of the water, the shank 31 lays extending along the water bottom surface S as shown in FIG. 7, owing to the weight of the metal chain 33 joined to the free end thereof. In this condition, the Danforth type anchor is pulled forward via the mooring rope 34 to move in an orientation in which the free end of the shank 31 is positioned in front, by moving the ship. At the same time, the anchor maintains its orientation in which the secondary guide plates 37 are positioned on the water bottom surface S, so that the sharp front end portions of the flukes 35, 35 are put in a sand-thrust state and further bit into the sand. As a result, the anchor itself is fixed to the bottom of the water, and enables the ship to be anchored.
At this time, the shank 31 is in the condition in which it has been turned by a certain angle from the reference direction.
In order to fix the Danforth type anchor reliably to the bottom of the water, the mooring rope 34 is usually set to have a length 3-5 times as long as the depth of the water. When the mooring rope 34 of such a length is put in a strained state while the ship is anchored, an angle made by the water bottom surface, which is parallel to the water surface, with the mooring rope 34 may become not larger than 20.degree.. As a result, the angle made by the shank 31 with the water bottom surface also may become small. Therefore, for example, even when the ship is moved by the wind, etc. to cause the mooring rope 34 to be put in a strained state, the Danforth type anchor is not extracted out from the water bottom but the fixed condition thereof is kept.
In order to fix the Danforth type anchor stably when the waves are high or when the wind is strong, it is effective to use a mooring rope 34 of a still greater length, for example, a length not smaller than five times the depth of the water, and thereby making the angle made by the shank 31 with the water surface smaller.
However, when the Danforth type anchor is fixed to the water bottom by using such a longer mooring rope 34, the area within which the ship may be moved on the water surface enlarges. Therefore, the position of the ship is not stabilized, and the possibility that the ship deviates greatly from, for example, an intended fishing point becomes large.
Under the circumstances, it is demanded that a Danforth type anchor capable of being fixed to the water bottom reliably even when the waves are high and the wind is strong be developed.